This application claims the priority of Korean Patent Application No. 2004-50480, filed on Jun. 30, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method of fabricating a laser diode, and more particularly, to a method of fabricating a laser diode, which can improve the optical characteristics of an InGaAsN quantum well (QW) layer.
2. Description of the Related Art
Nowadays, extensive research for applications of optical devices has progressed along with developments in high-speed data communications in the field of broad technologies including laser printers, optical image storage, underground optical cable systems, and optical communications.
Owing to the increased demand for more rapid and economical communication systems, optical fibers having broad transmission bands in a longer wavelength have been developed. Currently, optical fibers used in the wavelength range of 1.3 to 1.5 μm or higher are being developed.
To enable high-speed data transmission using an optical fiber, a laser oscillation signal having a wavelength range that coincides with the broad transmission band of the optical fiber should be needed so as to convert data into optical signals.
As a result, a GaAs-based vertical cavity surface emitting laser (VCSEL) diode was proposed. Since the GaAs-based VCSEL diode is economical and easily combines optical fibers, it becomes essential to a transmitter that performs high-level data link.
In addition, a result that long-wavelength laser oscillation can be embodied by adding nitrogen to a GaAs-based VCSEL is described by M. Kondow et al. in “Jpn. J. Appl. Phys., vol. 35(1996), pp. 1273–1275, Part 1, No. 2B, InGaAsN: A Novel Material for Long-Wavelength-Range Laser Diodes with Excellent High-Temperature Performance.”
After publishing the result of M. Kondow's research, laser diodes having the wavelength range of about 1.3 μm using InGaAsN have been laboriously developed in need of optical communication components used for metro area networks (MANs).
However, a recent paper describes that the optical characteristics of an InGaAsN QW layer are deteriorated due to the influence of Al (refer to Jpn. J. Appl. Phys., Vol. 43, No. 4A, 2004, pp. 1260–1263, “Al Contamination in InGaAsN Quantum Wells Grown by Metalorganic Chemical Vapor Deposition and 1.3 μm InGaAsN Vertical Cavity Surface Emitting Lasers”).
FIG. 1 is a flowchart illustrating a method of fabricating a conventional laser diode.
Referring to FIG. 1, a substrate is loaded into a deposition reactor A in operation 2, and a semiconductor material layer including Al, i.e., a first AlGaAs clad layer is formed on the substrate in operation 4. Then, the substrate is conveyed to a deposition reactor B. Next, a first GaAs barrier layer is formed on the first AlGaAs clad layer in operation 5, and an InGaAsN QW layer is formed on the first GaAs barrier layer in operation 6. Thereafter, a second GaAs barrier layer is formed on the InGaAsN QW layer in operation 7, and a second AlGaAs clad layer is formed on the second GaAs barrier layer in operation 8.
Al may adversely affect the optical characteristics of an InGaAsN QW layer particularly when a process of forming a semiconductor material layer, such as an AlGaAs clad layer or a distributed brag reflection (DBR) layer, and a process of forming the InGaAsN QW layer on the semiconductor material layer are performed in a single deposition reactor.
This is because when the InGaAsN QW layer is formed, Al remaining in the deposition reactor combines with N that is a source element of the InGaAsN QW layer so that the optical characteristics of the InGaAsN QW layer are degraded.
Accordingly, to minimize the influence of Al on the optical characteristics of the InGaAsN QW layer, the semiconductor material layer, such as the AlGaAs clad layer or the DBR layer, and the InGaAsN QW layer are formed in separate deposition reactors, respectively.
Another method for avoiding the influence of Al is to periodically clean a deposition reactor. That is, to remove Al accumulated in the deposition reactor during formation of an AlGaAs clad layer or a DBR layer, the entire deposition reactor needs to be periodically disassembled and cleaned.
However, this method requires an additional apparatus to increase cost and reduces process speed to lower efficiency. In addition, skilled human power is needed.
Further, since a layer forming process is stopped and then resumed, a semiconductor material layer may have defects or be contaminated with impurities, thus degrading the reproducibility or reliability of laser diodes.